1,720,961 research outputs found
Membrane Technologies for the Water Treatment. Part 1: Basic Principles
No full textMembrane technologies have become a key player among technologies
for the treatment and purification of water streams. Common applications are (i)
filtration for drinking water polishing; (ii) filtration as tertiary treatment in wastewater
treatment plants; (iii) reverse osmosis for freshwater production via desalination
of brackish and seawater, etc. All membrane technologies are based on the use of
selective membranes packed into membrane modules arranged into module racks,
eventually constituting a plant. The features of membrane materials, module geometry,
and plant configuration are fundamental to understanding the behaviour and
operational performance of the membrane separation process. In this chapter, an
overview of the fundamentals of membrane technologies is provided, spanning from
basic definitions, membrane materials, and fabrication techniques to module development
and transport phenomena governing the most important type of applications
for water treatment
Modelling of selective ion partitioning between ion-exchange membranes and highly concentrated multi-ionic brines
Full text linkIn recent years, the growing interest in the use of Ion-Exchange Membranes, in the treatment of highly concentrated multi-ionic brines for the selective recovery of critical elements, has prompted the research of fundamental models capable of predicting the IEMs selectivity towards like-charged species. Prior studies have proposed ion partitioning models limited to single-salt solutions that were validated only up to moderate salt concentrations. In this work, we developed a novel multi-ionic extension of the Manning counter-ion condensation model, aiming to predict the sorption selectivity of like-charged counter-ions. Furthermore, the peNRTL model was coupled with the extended Manning model to broaden its applicability range, encompassing membrane equilibrated with very highly concentrated solutions. Novel experimental ion sorption tests with single-salt and binary solutions including NaCl, KCl, MgCl2, and CaCl2 at high concentrations were performed with the commercial cation-exchange membrane Fumasep FKE-50. To the best of Authors’ knowledge, the proposed model for the first time successfully provided quantitative predictions of multi-ionic ion partitioning for all the systems investigated up to extremely high external salt concentrations. The outcomes of this work suggest a strong influence of the local non-electrostatic interactions on the activity coefficients in the membrane phase at high external concentration and highlight the key role of counter-ions hydration state in the condensation phenomenon
Current distribution along electrodialysis stacks and its influence on the current-voltage curve: behaviour from near-zero current to limiting plateau
Full text linkThe current maldistribution along the flow path of electrodialysis (ED) units is a well-known phenomenon.
However, it has been poorly quantified via experimental tests so far. This work aimed at measuring the current
distribution in an ED stack with 40 cm path length, provided with four-segment electrodes. The current-voltage
curve (CVC) of each segment was recorded under several operating conditions of inlet concentrations and feed
velocity. In the CVC of the first segment, the current increased approaching a saturation, while in that of the
remaining segments it passed through a maximum and then settled at near-zero values when high voltage values
were applied. The current fraction on the segments decreased from inlet to outlet. In the overall CVC's first
region, up to ~50 % of total current flowed through the first quarter of stack. As the voltage increased, the
current fraction increased in the first segment, while it decreased in the other ones tending to vanish. At the
limiting condition, the relative standard deviation of the current fraction distribution ranged from 40 % to 68 %.
This strong non-uniformity in the ED stack, which may represent one stage of an industrial plant, implies that the design of commercial units must be improved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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